1. Field of the Invention
The invention pertains to a process for producing castings such as engine blocks, etc., out of cast iron with lamellar graphite.
2. Description of the Related Art
Castings find use in nearly every branch of industry such as in machine tool construction, in semi-finished products, in the construction of furnaces and heating systems, in engine construction, and finally also in the chemical industry. To save weight, it is desirable to produce castings with thin walls but still with sufficient strength, but this requires that the molten cast iron have good flow behavior. It is known that an elevated carbon content promotes the flowability of the molten cast iron. The carbon content of the cast iron can be controlled by the make-up of the charge and by the way in which the furnace is operated. Cast iron is usually melted in a cupola furnace. Nevertheless, the melting process can also be carried out in a rotary furnace or in an electric furnace. After the melt has been poured, the casting usually remains in the mold until it has cooled to about 300.degree. C. The structural state achieved during this cooling process is usually accepted as is, even though it is known that effects can be exerted on the microstructural condition and thus on the mechanical properties of the casting by the use of certain cooling conditions. To achieve specific types of mechanical properties, it is conventional practice to produce alloyed cast iron by the addition of special additives such as copper, chromium, phosphorus, antimony, manganese, microalloys, etc.
For many types of castings, including especially the engine blocks of internal combustion engines, it is desirable for certain areas of the casting to be harder or to have higher strength values than other areas of the same casting.